Gas pipe pumping system

Abstract

 A module for incorporating in a gas pipeline comprises an electric motor 4 connected to an axial compressor 14 located in a pipe section 20 which is adapted to be connected into a main pipeline. A passage for the gas is formed in an annular passage between the motor 4 and the wall of the pipe section 20.
A plurality ofthe modules may be located in parallel with the main gas pipe line.

Description

[0001] This invention relates to apparatus for compressing gas in gas transmission pipelines such as the gas National Grid and the pipelines leading to the National Grid and Northsea gas fields.

[0002] For practical and, particularly, economic reasons, it is desirable to transmit gas a high pressure and to maintain gas pressure at a high level throughout the length of the pipe. However, as the gas gets further and further from the compression point its pressure naturally falls and it is therefore necessary to recompress the gas at intervals for onward transmission. The closer together the recompression points are the less the overall power consumption required, since the more frequent recompression, the higher t.he overall average gas pressure.

[0003] Current technology involves the use of large compression booster stations at relatively infrequent intervals. The compression usually is carried out by gas turbine powered compressors. Even on land, the provision of such booster stations causes problems because they are relatively expensive, requiring a permanent building and a large site having vehicular access. There are environmental problems not only with the appearance of the station but also with the waste gases, because, for maximum efficiency, gas turbines require a short chimney for exhausting the waste gases. Tall chimneys adversely affect the efficiency of gas turbines due to friction and turbulence in the exhaust ducts. Thus, the waste gases must be discharged relatively close to the ground which accentuates environmental problems.

[0004] There is, also, an inevitable amount of noise generated. These characteristics cause even greater problems in urban areas.

[0005] The economic and efficiency problems are even greater in undersea pipelines such as those in the North _Sea. This is because each booster station requires its own platform and such platforms are extremely expensive. In order to reduce the number of such platforms which are needed in a pipeline, the gas pressure in the pipe is allowed to fall between stations to a greater level than is desirable from a pumping efficiency aspect.

[0006] The present invention seeks to provide a solution to these problems.

[0007] According to the broadest aspect of the present invention, there is provided an in-line electric motor and compressor assembly adapted for mounting in - side a gas pipe line, the motor having passageways for the gas to pass therethrough or being such as to form in conjunction with the pipeline, an annulus defining a passage or passages for the gas between the motor and pipeline.

[0008] In a preferred embodiment to be described hereinafter, the motor comprises a squirrel cage electric induction motor, the compressor comprising a multi-stage axial compressor located upstream of said motor and being adapted to be driven thereby.

[0009] Preferably, the motor/compressor assembly is, in use, located in a length of pipe to form a modul-e adapted to be removably secured in a pipeline. The module may be secured coaxially in the pipeline but, alternatively, one or more modules may be located in by-passes in parallel with the pipeline.

[0010] A preferred embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which:

Figure 1 shows a motor/compressor assembly for incorporation in a gas pipeline.

Figure 2 shows a side view of the assembly of Figure 1 incorporated in a subsea module and

Figure 3 shows a schematic plan view of a subsea station incorporating two of the modules shown in Figure 2, arranged in parallel with the main gas pipeline.

[0011] Referring now to Figure 1 there is shown a standard gas transmission pipeline 1. The diameter of the pipe depends on the location of the pipeline in the gas transmission network and the projected volume of gas to be transmitted. Typically, with current technology, its diameter may be forty inches but, equally, may be less than ten. This particular application is intended primarily for undersea locations and therefore has a terminal box 2 secured to the exterior of the pipe 1, the terminal box including an anchorage point 3 for a marker buoy. An electric motor 4 is located within the pipe and power to drive the motor is supplied through a power cable which passes into the terminal box 2 through a pressure gland 6 for connection to the windings of the electric motor 4. The motor consists of a squirrel cage induction motor which is located substantially coaxially in the pipe on support webs 7 so as to provide an annular passageway 8 between the exterior of the motor and the pipe wall, through which gas can pass. The rotor 13 is supported on bearings 9 and 10 which are supplied with oil from a reservoir (as shown in Figure 2), by means of an oil pump 11 located at the downstream end of the motor.

[0012] The shaft 12 of the electric motor which carries the rotor 13 has an extension which is connected to a multi-stage axial compressor 14, the compressor being mounted on a thrust bearing 15 and front bearing 16.

[0013] Although the motor 4 is shown as being directly connected to the compressor 14, it will be understood that a gear box may be located between the two components although for installations such as under the North Sea, a direct connection is preferred in the interests of simplicity and reliability.

[0014] Referring now to Figure 2 there is shown a side view, partly sectioned, of a module for incorporation in a subsea pipeline. The module includes a pipe section 20 having, at its ends flanges 21 by which the pipe section 20 can be bolted to corresponding flanges 21a of the remainder of the pipeline as shown in Figure 3. The pipe section 20 includes a motor/compressor assembly as shown in Figure 1. Reference 22 is the oil tank, to which previous mention has been made, which supplies oil through oil pipes 23 to the bearings of the motor compressor assembly. A compressor blow off valve 24 is secured to the pipe line 20 adjacent the compressor.

[0015] Adjacent each end of the pipe section 20, there are located respective glandless compressor isolating valves 25. As shown in the left hand side of Figure 2, these valves contain a valve closure member 26, powered by an electric motor 27, for closing the pipe section 20.

[0016] Referring now to Figure 3 there is shown a schematic plan view of a subsea compressor station incorporating two of the compressor modules shown in Figure 2, arranged in parallel. The two modules are located in parallel with each other and with a main pipeline 28. The main pipeline includes a blocking valve 29 which is closed to divert the gas flow through the compressor modules. The main pipeline 28 also includes a blow off isolating valve 30 which is connected to corresponding blow off valves 31 in the pipe section 20 of the two modules through pipes 32.

[0017] As mentioned earlier, the pipe sections 20 of the modules are connected by their end flanges 21 to corresponding flanges 21a of the main pipeline. In this embodiment, the flanges 21a are located on branch pipe sections 33.

[0018] Adjacent the flanges 21a of each of the branch sections 33 there is located a glandless pipeline isolating valve 34.

[0019] By appropriately opening and closing the isolating valves 25, 29 and 34, it is possible to control the flow of gas selectively through the required section or sections of the station. If for example, the gas pressure is such that boosting is not required, the valve 29 would be opened and the valves 25 and 34 closed. The gas would then flow uninterrupted along the main section 28 of the pipeline. If only one compressor is required to give the required pressure boost, then only one need be brought into operation by opening the appropriate ones of the valves 25, 34, with the valve 29 closed.

[0020] The isolating valves 25 and 34 are also used during maintenance. With these valves and the valve 29 closed, the modules can be detached from the pipeline by unbolting their flanges 21 and the module removed without any significant quantity of seawater entering the pipeline or the interior of the module. This arrangement has the further advantage that a faulty module can be simply replaced by another module with the minimum of downtime.

[0021] Although this embodiment describes a module for use in North Sea pipelines, the present invention also has particular advantages in land based operations. As mentioned earlier, the provision of infrequent large gas turbine booster has disadvantages whereas booster stations incorporating the present invention do not require large sites since the they can be provided in a small pit, for example, placed on public land alongside roads. There are thus enormous cost savings both in the reduced infra-structure which is required and also in the increased efficiency of gas transmission since the modules can be located more easily, precisely where they are required. If the power required cannot be provided by a single motor, then a plurality of motors connected in series may be provided. Furthermore, each module may incorporate more than one motor/compressor assembly.

[0022] Although the invention has been described as having an electric motor driving a compressor it is to be under- sttod that the invention is also applicable to a reversed arrangement in which an impeller drives an electric generator. Such an installation would be particularly useful where a reduction in gas pressure is required such as occurs when a branch line is connected to a main transmission line. Conventionally, in such circumstances a reducing valve is incorporated in the pipeline but this involves a cost penalty since, as the gas is reduced in pressure, it naturally contains less energy and the difference in energy level is waste. By using the present invention the pressure reduction is obtained at least partially by driving the impeller and is converted to useful electrical energy by the generator which can either be fed back to the National Grid or used for immediate purposes. The present invention has the advantage that the motor and compressor can be located in standard sized pipework which not only obviates the cost of manufacturing special sized pipes but also facilitates its incorporation into both new and existing pipelines.

[0023] Although the module described utilises bolted flanges for securing it in the pipeline it will be understood that other methods can be used. For example, for undersea locations welded joints may be used, but many types of joining/sealing may be used.

Claims

1. An in-line electric motor and compressor assembly adapted for mounting in-side a gas pipe line, the motor having passageways for the gas to pass therethrough or being such as to form in conjunction with the pipeline an annulus defining a passage or passages for the gas between the motor and pipeline.

2. An assembly according to claim 1 wherein the motor comprises a squirrel cage electric induction motor, the compressor comprising a multi-stage axial compressor located upstream of said motor and being adapted to be driven thereby.

3. An in-line electric generator and pump assembly adapted for mounting inside a gas pipeline, the generator having passageways for the gas to pass therethrough or being such as to form, in conjunction with the pipeline, an annulus defining a passage or passages for the gas between the generator and the pipeline.

4. An assembly according to claim 1, 2 or 3 wherein the motor and compressor, or the generator and pump, incorporate oil lubricated bearings fed with oil from an oil reservoir.

5. A module adapted for incorporation in a pipeline comprising an assembly according to claim 1, 2 or 3 or 4 located in a pipe section adapted to be secured in a pipeline.

6. A module according to claim 5 including means to removably secure the module to said pipeline.

7. A module according to claim 5 or 6 adapted to be secured co-axially in said pipeline.

8. An assembly including a plurality of modules according to claim 5 or 6, said plurality of modules comprising by-passes arranged in parallel with the pipeline.

9. An assembly according to claim 8 wherein each module incorporates isolating valves operable to seal the module interior, further isolating valves being located in each by - pass and operable to close access to the pipeline.

10. An assembly according to claim 9 wherein said isolating valves comprise electrically powered glandless valves.

11. An assembly according to claim 8, 9 or 10 wherein diverter valve means is located in a pipeline part in parallel with said modules and is operable to close said pipeline part to divert gas flow through said modules.

12. An assembly for incorporation in a gas pipeline, incorporating an electric motor and a compressor, or a pump aαd electric generator. substantially as described herein with reference to and as illustrated in the accompanying drawings

Drawing